Hemodialysis is a medical procedure that uses an external medical device to clean the blood of people who have experienced complete or partial renal failure. This procedure is typically done 3 times a week and allows patients with renal failure to survive and to lead almost normal lives. Besides kidney transplantation, hemodialysis is the only procedure available today that allows long-term survival of patients with failed kidneys. In the United States, there are approximately 450,000 patients on hemodialysis, and there are approximately 1.7 million patients on hemodialysis worldwide. More than half of the patients starting hemodialysis use a tunneled hemodialysis catheter as a vascular access. Every year in the United States, approximately 500,000 hemodialysis catheter procedures are performed, half of which involve placement or exchange of a hemodialysis catheter. Similarly, there are approximately 2 million hemodialysis procedures performed annually worldwide, most of which involve placement or exchange of the hemodialysis catheter. While a variety of hemodialysis catheters are available, hemodialysis catheters are generally comprised of two tubes, each with a lumen aperture disposed at its end. One tube carries out of the patient blood that needs to be cleaned, while the other returns cleaned blood to the patient.
A common problem with hemodialysis catheters is formation of a fibrous sheath on the exterior surface of the catheter. The name fibrous sheath is somewhat of a misnomer. A mature fibrous sheath (one that has developed for more than 1-2 weeks from catheter insertion) is mainly formed of smooth muscle cells and collagen. The fibrous sheath looks like a thin but resilient layer of material (like cellophane) that surrounds the catheter and blocks the apertures of the lumens, thereby impeding the blood flow needed for an adequate hemodialysis.
A fibrous sheath's composition is very different from that of a thrombus. A thrombus, sometimes referred to as a clot, is composed of blood platelets and results from blood coagulation. Thrombolytic therapy to remove thrombi typically involves the use of medications to dissolve the thrombi. In contrast to thrombi, the above-described fibrous sheaths are composed of smooth muscle cells and collagen, and such fibrous sheaths do not respond to thrombolytic therapy due to the different compositions of fibrous sheaths and thrombi. Instead, other methods are required to disrupt or destroy fibrous sheaths.
Fibrous sheath formation starts as early as 24 hours after insertion of the catheter, and the composition of the fibrous sheath changes as the catheter remains implanted in the patient. The sheath begins as a thrombus in the first few days and rapidly transforms into a combination of smooth muscle cells and collagen deposition covered by endothelial cells after 1-2 weeks. After 4 weeks, the smooth muscle cells change to a contractile phenotype and the amount of collagen deposition is increased.
Fibrous sheaths are known to form around most hemodialysis catheters and also around other devices placed inside the human body such as pacemaker wires, pacemaker boxes, and breast implants. Fibrous sheath formation is especially problematic for implanted catheters that are designed to stay implanted in a patient for months at a time. The fibrous sheath forms around all hemodialysis catheters, causing dysfunction in a significant number of them. In fact, this type of catheter dysfunction accounts for nearly half of all procedures involving the exchange of implanted hemodialysis catheters. In these circumstances, the hemodialysis catheter is removed and the fibrous sheath is obliterated by inflation of an angioplasty balloon inside the sheath. Thereafter, a new catheter is placed inside the patient. This procedure is risky and is very expensive because it is done in sterile conditions, in fluoroscopy (X-ray)-equipped procedure rooms by specially trained doctors and nurses with the patient under conscious sedation.
U.S. Patent Application Publication No. 2008/0306427 A1 describes a catheter device having a shaft, a first lumen extending through the shaft, and a second lumen extending through the shaft. An opening to the first lumen is at a distal end of a shaft and an opening to the second lumen is offset from the opening to the first lumen and positioned further up the shaft in a direction towards a proximal end of the shaft. A balloon is attached to an outer surface of the shaft and is positioned proximate to the opening of the second lumen. The balloon is inflated in an effort to prevent an occluding material from occluding the opening of the first lumen and the opening of the second lumen.